Communication method and apparatus applied to multi-link device in wireless local area network

ABSTRACT

This application provides a communication method, an access network device, a terminal device, and a core network device. In a process in which the terminal device is handed over from a first access network device to a second access network device, the second access network device learns of first service progress of the first access network device based on a first sequence number of a data packet forwarded by the first access network device, without introducing additional progress exchange information between the two access network devices.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/CN2021/081772, filed on Mar. 19, 2021, which claims priority toChinese Patent Application No. 202010203782.4, filed on Mar. 20,2020.The disclosures of the aforementioned applications are herebyincorporated by reference in their entireties.

BACKGROUND

A multimedia broadcast multicast service (Multimedia Broadcast MulticastService, MBMS) is a service oriented to a plurality of terminal devices.For example, a live broadcast service and some public safety serviceseach are the MBMS service. In a current communication system, an accessnetwork device may send the MBMS service to the terminal device in aunicast transmission mode by establishing a dedicated bearer with thesingle terminal device, or may send the MBMS service to the terminaldevices in a multicast (groupcast) transmission mode by establishing acommon bearer with the plurality of terminal devices. Regardless of theunicast transmission mode or the multicast transmission mode, differentaccess network devices separately determine sequence numbers of datapackets of MBMS services when sending the data packets of the MBMSservices to terminal devices within coverage of the different accessnetwork devices.

When moving from a source access network device to a target accessnetwork device, to continue to receive an MBMS service, after beinghanded over to the target access network device, a terminal device needsto continue to receive an MBMS service originally received from thesource access network device. However, because progress of MBMS servicessent by the two access network devices may be inconsistent, and thesource access network device and the target access network device areindependent of each other when determining sequence numbers of datapackets of the MBMS services, the source access network device and thetarget access network device may have inconsistent understanding of thesequence numbers of the data packets of the MBMS services in a handoverprocess of the terminal device. Consequently, when the handover occurs,receiving of the MBMS service by the terminal device is interrupted, orthe terminal device receives a redundant data packet. Therefore,continuity of the MBMS service cannot be ensured.

SUMMARY

At least one embodiment provides a communication method, an accessnetwork device, a terminal device, and a core network device. Accordingto the communication method, a conventional-technology case in which aterminal device receiving an MBMS service receives a redundant datapacket or service data is interrupted during handover between accessnetwork devices because multicast service progress of the differentaccess network devices is inconsistent.

According to a at least embodiment, a communication method is provided.The method is applied to a first access network device, and includes:

receiving a first data packet and first indication information from acore network device, where the first indication information indicates asequence of the first data packet in at least one data packet;determining a first sequence number of a first protocol layer of thefirst data packet based on the first indication information; and sendingthe first data packet to a terminal device.

Therefore, in a process in which the terminal device is handed over fromthe first access network device to a second access network device, thesecond access network device learns of first service progress of thefirst access network device based on a sequence number of a data packetforwarded by the first access network device, without introducingadditional progress exchange information between the two access networkdevices.

With reference to at least one embodiment, in some embodiments, thefirst indication information includes at least one of the followinginformation: a general packet radio service tunneling protocol-userplane GTP-U sequence number and a first service sequence number, wherethe first service sequence number is set by the core network device or adata server, the first data packet is a data packet of a first service,and the at least one data packet is a data packet of the first service.

In some embodiments, the first protocol layer includes at least one ofthe following: a service data adaptation protocol SDAP layer, a packetdata convergence protocol PDCP layer, and a radio link control layer RLClayer.

In some embodiments, the method further includes: setting a startsequence number of the first protocol layer of the first data packetbased on the first indication information in response to any one ofestablishment of a first protocol entity, re-establishment of the firstprotocol entity, and recovery of the first protocol entity occurs.

Therefore, in response to any one of the establishment of the firstprotocol entity, the re-establishment of the first protocol entity, andthe recovery of the first protocol entity occurs, the first accessnetwork device sets the start sequence number of the first protocollayer of the first data packet based on the first indicationinformation, to ensure continuity of data packets of the first service,and avoid sequence discontinuity that is of the data packets of thefirst service and that is caused by setting of the start sequence numberof the first protocol layer.

In some embodiments, the method further includes: sending secondindication information to the terminal device, where the secondindication information indicates a sequence number of the first datapacket that is of the first service and that is sent by the first accessnetwork device to the terminal device after the first protocol entity isestablished, the first protocol entity is re-established, or the firstprotocol entity is recovered.

Therefore, the terminal device determines a start sequence number of afirst protocol layer of the first received data packet based on thesecond indication information, so that a data packet loss caused byinconsistent determining of the first data packet by the first terminaldevice and the first access network device is avoided.

In some embodiments, the method further includes: receiving thirdindication information from a second access network device, where thethird indication information indicates the first access network deviceto stop forwarding a data packet to the second access network device;and stopping, based on the third indication information, forwarding thedata packet to the second access network device.

Therefore, in a handover process of the first terminal device, thesecond access network device determines whether data forwarding of thefirst access network device is stopped, and sends the data forwardingstop indication information to the first access network device, so thatmulticast service receiving continuity of the terminal device in thehandover process is ensured, and a packet loss or redundant transmissionis avoided.

In some embodiments, the method further includes: receiving fourthindication information sent by the second access network device, wherethe fourth indication information indicates a sequence number of thefirst data packet forwarded by the first access network device to thesecond access network device; and forwarding a data packet to the secondaccess network device based on the fourth indication information.

The fourth indication information indicates a sequence number of a firstprotocol layer of the first data packet that is not received by thefirst terminal device, namely, a start data packet in data forwardingperformed by the first access network device. In this way, the firstterminal device can be prevented from receiving a redundant data packet.To be specific, the following case can be avoided: A data packet sent bythe first access network device is successfully received by the firstterminal device, but is still forwarded by the first access networkdevice to the second access network device, and then sent by the secondaccess network device to the first terminal device.

In some embodiments, the method further includes: receiving fifthindication information sent by a second access network device, where thefifth indication information includes a second sequence number N, andthe second sequence number indicates a sequence number of the first datapacket that is of the first service and that is sent by the secondaccess network device to the terminal device after handover of theterminal device is completed. In response to a sequence number that isof a protocol layer and that corresponds to a data packet successfullyis sent by the first access network device to the terminal device isN-1, the first access network device stops sending a data packet to theterminal device.

Therefore, in a handover process, the first access network devicedetermines, based on the SN indicated by the second access networkdevice, when to stop a connection to the terminal device, so thatmulticast service receiving continuity of the terminal device in thehandover process is ensured, and a packet loss or redundant transmissionis avoided.

In some embodiments, the first access network device sends stopindication information to the second access network device, to indicatethe first access network device to disconnect from the first terminaldevice.

In some embodiments, the second access network device sends fifthindication information to the first access network device, where thefifth indication information includes a second sequence number N-1, andthe second sequence number indicates the first access network device tostop, in response to a sequence number of a first protocol layer of adata packet successfully sent by the first access network device to theterminal device is N-1, sending a data packet to the terminal device.

Therefore, the first access network device no longer performscalculation, and directly stops sending the data packet after a datapacket whose first sequence number is N-1 is sent.

According to a second aspect, a communication method is provided. Themethod is applied to a terminal device, and includes: receiving secondindication information from a first access network device, where thesecond indication information indicates a sequence number of the firstdata packet that is of a first service and that is sent by the firstaccess network device to the terminal device after a first protocolentity is established, the first protocol entity is re-established, orthe first protocol entity is recovered.

With reference to the second aspect, in some embodiments of the anotheraspect, the method further includes: in response to the first protocolentity is re-established or recovered, sending request information tothe first access network device, where the request information requeststhe first access network device to send the sequence number of the firstdata packet that is of the first service and that is sent by the firstaccess network device to the terminal device after the first protocolentity is re-established or the first protocol entity is recovered.

With reference to the second aspect, in some embodiments of the secondaspect, the method further includes: sending status report informationof a data packet to a second access network device, where the statusreport information of the data packet indicates, to the second accessnetwork device, a data packet successfully received by the terminaldevice and a data packet unsuccessfully received by the terminal device,where the terminal device is handed over from the first access networkdevice to the second access network device.

According to a third aspect, a communication method is provided. Themethod is applied to a second access network device, and includes:receiving a first data packet and first indication information from acore network device, where the first indication information indicates asequence of the first data packet in at least one data packet;determining a second sequence number of a first protocol layer of thefirst data packet based on the first indication information; and sendingthe first data packet to a first terminal device.

With reference to the third aspect, in some embodiments of the thirdaspect, the first indication information includes at least one of thefollowing information: a general packet radio service tunnelingprotocol-user plane GTP-U sequence number and a first service sequencenumber, where the first service sequence number is set by the corenetwork device or a data server, the first data packet is a data packetof a first service, and the at least one data packet is a data packet ofthe first service.

With reference to the third aspect, in some embodiments of the thirdaspect, the first protocol layer includes at least one of the following:

a service data adaptation protocol SDAP layer, a packet data convergenceprotocol PDCP layer, and a radio link control layer RLC layer.

With reference to the third aspect, in some embodiments of the thirdaspect, the method further includes: setting a start sequence number ofthe first protocol layer of the first data packet based on the firstindication information in response to any one of establishment of afirst protocol entity, re-establishment of the first protocol entity,and recovery of the first protocol entity occurs.

With reference to the third aspect, in some embodiments of the thirdaspect, the method further includes: sending second indicationinformation to the terminal device, where the second indicationinformation indicates a sequence number of the first data packet that isof the first service and that is sent by a first access network deviceto the terminal device after the first protocol entity is established,the first protocol entity is re-established, or the first protocolentity is recovered.

With reference to the third aspect, in some embodiments of the thirdaspect, the method further includes: receiving a data packet from afirst access network device, where a second terminal device connected tothe first access network device is handed over from the first accessnetwork device to the second access network device, both the firstterminal device and the second terminal device perform the firstservice, and the data packet sent by the first access network device isa data packet of the first service; and sending third indicationinformation to the first access network device in response to a secondsequence number of a first protocol layer of a data packet that is beingsent to the first terminal device being greater than or equal to a firstsequence number of a first protocol layer of the data packet that issent by the first access network device, where the third indicationinformation indicates the first access network device to stop forwardinga data packet to the second access network device.

With reference to the third aspect, in some embodiments of the thirdaspect, the method further includes: receiving status report informationof a data packet from the second terminal device, where the statusreport information of the data packet indicates, to the second accessnetwork device, a data packet successfully received by the terminaldevice and a data packet unsuccessfully received by the terminal device;and sending fourth indication information to the first access networkdevice based on the status report information, where the fourthindication information indicates a sequence number of the first datapacket forwarded by the first access network device to the second accessnetwork device.

With reference to the third aspect, in some embodiments of the thirdaspect, the method further includes: sending fifth indicationinformation to a first access network device, where the fifth indicationinformation includes a second sequence number N, and the second sequencenumber indicates a sequence number of the first data packet that is ofthe first service and that is sent by the second access network deviceto a second terminal device after handover of the second terminal deviceis completed.

According to a fourth aspect, a communication method is provided. Themethod is applied to a core network device, and includes: receiving afirst data packet sent by a data server; sending a second data packetand first indication information to a first access network device, wherethe first indication information indicates a sequence of the second datapacket in at least one data packet sent by the core network device; andsending a third data packet and second indication information to asecond access network device, where the first indication informationindicates a sequence of the third data packet in the at least one datapacket of the core network device, where data in the second data packetand data in the third data packet are the same as data in the first datapacket.

With reference to the fourth aspect, in some embodiments of the fourthaspect, the first indication information includes at least one of thefollowing information: a general packet radio service tunnelingprotocol-user plane GTP-U sequence number and a first service sequencenumber, where the first service sequence number is set by the corenetwork device or the data server, the first data packet is a datapacket of a first service, and the at least one data packet is a datapacket of the first service.

According to a fifth aspect, an access network device is provided. Theaccess network device is a first access network device, a chip or amodule in the first access network device, or a chip or a system onchip. The access network device includes: a transceiver unit, configuredto receive a first data packet and first indication information from acore network device, where the first indication information indicates asequence of the first data packet in at least one data packet; and aprocessing unit, configured to determine a first sequence number of afirst protocol layer of the first data packet based on the firstindication information, where the transceiver unit is further configuredto send the first data packet to a terminal device.

With reference to the fifth aspect, in some embodiments of the fifthaspect, the first indication information includes at least one of thefollowing information: a general packet radio service tunnelingprotocol-user plane GTP-U sequence number and a first service sequencenumber, where the first service sequence number is set by the corenetwork device or a data server, the first data packet is a data packetof a first service, and the at least one data packet is a data packet ofthe first service.

With reference to the fifth aspect, in some embodiments of the fifthaspect, the first protocol layer includes at least one of the following:a service data adaptation protocol SDAP layer, a packet data convergenceprotocol PDCP layer, and a radio link control layer RLC layer.

With reference to the fifth aspect, in some embodiments of the fifthaspect, the processing unit is further configured to determine a startsequence number of the first protocol layer of the first data packetbased on the first indication information in response to any one ofestablishment of a first protocol entity, re-establishment of the firstprotocol entity, and recovery of the first protocol entity occurs.

With reference to the fifth aspect, in some embodiments of the fifthaspect, the transceiver unit is further configured to send secondindication information to the terminal device, where the secondindication information indicates a sequence number of the first datapacket that is of the first service and that is sent by the first accessnetwork device to the terminal device after the first protocol entity isestablished, the first protocol entity is re-established, or the firstprotocol entity is recovered.

With reference to the fifth aspect, in some embodiments of the fifthaspect, the transceiver unit is further configured to receive thirdindication information from a second access network device, where thethird indication information indicates the first access network deviceto stop forwarding a data packet to the second access network device;and the processing unit is configured to stop, based on the thirdindication information, forwarding the data packet to the second accessnetwork device.

With reference to the fifth aspect, in some embodiments of the fifthaspect, the transceiver unit is further configured to receive fourthindication information sent by the second access network device, wherethe fourth indication information indicates a sequence number of thefirst data packet forwarded by the first access network device to thesecond access network device; and the processing unit is configured toforward a data packet to the second access network device based on thefourth indication information.

With reference to the fifth aspect, in some embodiments of the fifthaspect, the transceiver unit is further configured to receive fifthindication information sent by a second access network device, where thefifth indication information includes a second sequence number N, andthe second sequence number indicates a sequence number of the first datapacket that is of the first service and that is sent by the secondaccess network device to the terminal device after handover of theterminal device is completed; and the processing unit is configured todetermine to stop, in response to a sequence number that is of aprotocol layer and that corresponds to a data packet successfully sentby the first access network device to the terminal device being N-1,sending a data packet to the terminal device.

According to a sixth aspect, a terminal device is provided. The terminaldevice is a terminal device, is a chip or a module in the terminaldevice, or is a chip or a system on chip. The terminal device includes atransceiver unit, configured to receive second indication informationsent by a first access network device, where the second indicationinformation indicates a sequence number of the first data packet that isof a first service and that is sent by the first access network deviceto the terminal device after a first protocol entity is established, thefirst protocol entity is re-established, or the first protocol entity isrecovered.

With reference to the sixth aspect, in some embodiments of the sixthaspect, the transceiver unit is further configured to: in response tothe first protocol entity is re-established or recovered, send requestinformation to the first access network device, where the requestinformation requests the first access network device to send thesequence number of the first data packet that is of the first serviceand that is sent by the first access network device to the terminaldevice after the first protocol entity is re-established or the firstprotocol entity is recovered.

With reference to the sixth aspect, in some embodiments of the sixthaspect, the transceiver unit is further configured to send status reportinformation of a data packet to a second access network device, wherethe status report information of the data packet indicates, to thesecond access network device, a data packet successfully received by theterminal device and a data packet unsuccessfully received by theterminal device, where the terminal device is handed over from the firstaccess network device to the second access network device.

According to a seventh aspect, an access network device is provided. Theaccess network device is a second access network device, a chip or amodule in the second access network device, or a chip or a system onchip. The access network device includes: a transceiver unit, configuredto receive a first data packet and first indication information from acore network device, where the first indication information indicates asequence of the first data packet in at least one data packet; and aprocessing unit, configured to determine a second sequence number of afirst protocol layer of the first data packet based on the firstindication information, where the transceiver unit is configured to sendthe first data packet to a first terminal device.

With reference to the seventh aspect, in some embodiments of the seventhaspect, the first indication information includes at least one of thefollowing information: a general packet radio service tunnelingprotocol-user plane GTP-U sequence number and a first service sequencenumber, where the first service sequence number is set by the corenetwork device or a data server, the first data packet is a data packetof a first service, and the at least one data packet is a data packet ofthe first service.

With reference to the seventh aspect, in some embodiments of the seventhaspect, the first protocol layer includes at least one of the following:a service data adaptation protocol SDAP layer, a packet data convergenceprotocol PDCP layer, and a radio link control layer RLC layer.

With reference to the seventh aspect, in some embodiments of the seventhaspect, the processing unit is further configured to set a startsequence number of the first protocol layer of the first data packetbased on the first indication information in response to any one ofestablishment of a first protocol entity, re-establishment of the firstprotocol entity, and recovery of the first protocol entity occurs.

With reference to the seventh aspect, in some embodiments of the seventhaspect, the transceiver unit is further configured to send secondindication information to the terminal device, where the secondindication information indicates a sequence number of the first datapacket that is of the first service and that is sent by a first accessnetwork device to the terminal device after the first protocol entity isestablished, the first protocol entity is re-established, or the firstprotocol entity is recovered.

With reference to the seventh aspect, in some embodiments of the seventhaspect, the transceiver unit is further configured to: receive a datapacket sent by a first access network device, where a second terminaldevice connected to the first access network device is handed over fromthe first access network device to the second access network device,both the first terminal device and the second terminal device performthe first service, and the data packet sent by the first access networkdevice is a data packet of the first service; and send third indicationinformation to the first access network device in response to a secondsequence number of a first protocol layer of a data packet that is beingsent to the first terminal device being greater than or equal to a firstsequence number a first protocol layer of the data packet that is sentby the first access network device, where the third indicationinformation indicates the first access network device to stop forwardinga data packet to the second access network device.

With reference to the seventh aspect, in some embodiments of the seventhaspect, the transceiver unit is further configured to: receive statusreport information that is of a data packet and that is sent by thesecond terminal device, where the status report information of the datapacket indicates, to the second access network device, a data packetsuccessfully received by the terminal device and a data packetunsuccessfully received by the terminal device; and send fourthindication information to the first access network device based on thestatus report information, where the fourth indication informationindicates a sequence number of the first data packet forwarded by thefirst access network device to the second access network device.

With reference to the seventh aspect, in some embodiments of the seventhaspect, the transceiver unit is further configured to send fifthindication information to a first access network device, where the fifthindication information includes a second sequence number N, and thesecond sequence number indicates a sequence number of the first datapacket that is of the first service and that is sent by the secondaccess network device to a second terminal device after handover of thesecond terminal device is completed.

According to an eighth aspect, a core network device is provided. Thecore network device is a core network device, a chip or a module in thecore network device, or is a chip or a system on chip. The core networkdevice includes a transceiver unit, configured to receive a first packetsent by a data server, where the transceiver unit is configured to senda second data packet and first indication information to a first accessnetwork device, where the first indication information indicates asequence of the second data packet in at least one data packet sent bythe core network device; and the transceiver unit is configured to senda third data packet and second indication information to a second accessnetwork device, where the first indication information indicates asequence of the third data packet in the at least one data packet sentby the core network device, where data in the second data packet anddata in the third data packet are the same as data in the first datapacket.

With reference to the eighth aspect, in some embodiments of the eighthaspect, the first indication information includes at least one of thefollowing information: a general packet radio service tunnelingprotocol-user plane GTP-U sequence number and a first service sequencenumber, where the first service sequence number is set by the corenetwork device or the data server, the first data packet is a datapacket of a first service, and the at least one data packet is a datapacket of the first service.

According to a ninth aspect, a communication apparatus is provided, andincludes a processor. The processor is connected to a memory. The memoryis configured to store a computer program. The processor is configuredto execute the computer program stored in the memory, to enable theapparatus to perform the method according to at least one embodiment,the method according to any one of the second aspect or the embodimentsof the second aspect, the method according to any one of the thirdaspect or the embodiments of the third aspect, or the method accordingto any one of the fourth aspect or the embodiments of the fourth aspect.

According to a tenth aspect, a computer-readable storage medium isprovided. The computer-readable storage medium stores a computerprogram. In response to the computer program is run, the methodaccording to at least one embodiment, the method according to any one ofthe second aspect or the embodiments of the second aspect, the methodaccording to any one of the third aspect or the embodiments of the thirdaspect, or the method according to any one of the fourth aspect or theembodiments of the fourth aspect is implemented.

According to an eleventh aspect, a chip is provided, and includes aprocessor and an interface. The processor is configured to readinstructions to perform the method according to at least one embodiment,the method according to any one of the second aspect or the embodimentsof the second aspect, the method according to any one of the thirdaspect or the embodiments of the third aspect, or the method accordingto any one of the fourth aspect or the embodiments of the fourth aspect.

In some embodiments, the chip further includes a memory. The memorystores instructions. The processor is configured to execute theinstructions stored in the memory or other instructions.

According to a twelfth aspect, a communication system is provided. Thesystem includes an apparatus that has a function of implementing themethods and the designs according to at least one embodiment, anapparatus that has a function of implementing the methods and thedesigns in the second aspect, an apparatus that has a function ofimplementing the methods and the designs in the third aspect, and anapparatus that has a function of implementing the methods and thedesigns in the fourth aspect.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of an application scenario according tosome embodiments described herein;

FIG. 2 is a schematic flowchart of a communication method according tosome embodiments disclosed herein;

FIG. 3 is a schematic flowchart of a method for handing over a terminaldevice between access network devices in a conventional technology;

FIG. 4 is a schematic diagram of an application scenario of a multicastservice according to some embodiments disclosed herein;

FIG. 5 is a schematic flowchart of a communication method according tosome embodiments disclosed herein;

FIG. 6 is a schematic flowchart of data forwarding in a communicationmethod according to some embodiments disclosed herein;

FIG. 7 is a schematic flowchart of a communication method according tosome embodiments disclosed herein;

FIG. 8 is a schematic block diagram of a communication apparatusaccording to some embodiments disclosed herein;

FIG. 9 is a schematic diagram of a structure of a terminal deviceaccording to some embodiments disclosed herein; and

FIG. 10 is a schematic diagram of a structure of an access networkdevice according to some embodiments disclosed herein.

DESCRIPTION OF EMBODIMENTS

The following describes technical solutions disclosed hereinwithreference to accompanying drawings.

To better understand the embodiments disclosed herein, terms that appearin embodiments are first explained.

The technical solutions in embodiments are be applied to variouscommunication systems, for example, a global system for mobilecommunications (global system for mobile communications, GSM) system, acode division multiple access (code division multiple access, CDMA)system, a wideband code division multiple access (wideband code divisionmultiple access, WCDMA) system, a general packet radio service (generalpacket radio service, GPRS) system, a long term evolution (long termevolution, LTE) system, an LTE frequency division duplex (frequencydivision duplex, FDD) system, an LTE time division duplex (time divisionduplex, TDD) system, a universal mobile telecommunication system(universal mobile telecommunication system, UMTS), a worldwideinteroperability for microwave access (worldwide interoperability formicrowave access, WiMAX) communication system, a 5th generation (5thgeneration, 5G) system, or a new radio (new radio, NR) system. Inaddition, the technical solutions is alternatively be applied to asubsequent evolved system, for example, a 6th generation 6Gcommunication system or even a more advanced 7th generation 7Gcommunication system.

A terminal device in embodiments is also be referred to as a userequipment (user equipment, UE), a mobile station (mobile station, MS), amobile terminal (mobile terminal, MT), an access terminal, a subscriberunit, a subscriber station, a remote station, a remote terminal, amobile device, a user terminal, a terminal, a wireless communicationdevice, a user agent, a user apparatus, or the like.

The terminal device is a wireless terminal or a wired terminal. Thewireless terminal refers to a device that provides a user with voiceand/or other service data connectivity, a handheld device with awireless connection function, or another processing device connected toa wireless modem. The wireless terminal communicates with one or morecore networks through a radio access network (Radio Access Network,RAN). The wireless terminal is a mobile terminal, for example, a mobilephone (which is also referred to as a “cellular” phone), and a computerhaving the mobile terminal, for example, a portable, pocket-sized,handheld, computer built-in, or in-vehicle mobile apparatus, whichexchanges voice and/or data with the radio access network. For example,the wireless terminal is a device such as a personal communicationsservice (Personal Communication Service, PCS) phone, a cordlesstelephone set, a session initiation protocol (Session InitiationProtocol, SIP) phone, a wireless local loop (Wireless Local Loop, WLL)station, or a personal digital assistant (Personal Digital Assistant,PDA). The wireless terminal is also be referred to as a system, asubscriber unit (Subscriber Unit), a subscriber station (SubscriberStation), a mobile station (Mobile Station), a mobile station (Mobile),a remote station (Remote Station), a remote terminal (Remote Terminal),an access terminal (Access Terminal), a user terminal (User Terminal), auser agent (User Agent), a user equipment (User Device or UserEquipment), a mobile internet device (mobile internet device, MID), awearable device, a virtual reality (virtual reality, VR) device, anaugmented reality (augmented reality, AR) device, a wireless terminal inindustrial control (industrial control), a wireless terminal in selfdriving (self driving), a wireless terminal in remote surgery (remotemedical surgery), a wireless terminal in a smart grid (smart grid), awireless terminal in transportation safety (transportation safety), awireless terminal in a smart city (smart city), a wireless terminal in asmart home (smart home), and a vehicle-mounted device, a wearabledevice, a terminal device in a 5G network, a terminal device in a futureevolved public land mobile network (public land mobile network, PLMN),or the like. This is not limited in embodiments disclosed herein.

By way of example but not limitation, in embodiments disclosed herein,the wearable device is also be referred to as a wearable intelligentdevice, and is a generic term for wearable devices such as glasses,gloves, watches, clothes, and shoes that are developed based onintelligent design of daily wearing by using wearable technologies. Thewearable device is a portable device that is directly worn or integratedinto clothes or an accessory of a user. The wearable device is not onlya hardware device, but also implements a powerful function throughsoftware support, data exchange, and cloud interaction. Generalizedwearable intelligent devices include full-featured and large-sizedevices that can implement complete or partial functions withoutdepending on smartphones, for example, smart watches or smart glasses,and devices that focus only on one type of application function and towork with other devices such as smartphones, for example, various smartbands or smart jewelry for monitoring physical signs.

In addition, in embodiments disclosed herein, the terminal device isalternatively be a terminal device in an internet of things (internet ofthings, IoT) system. An IoT is an important component of futureinformation technology development. A main technical feature of the IoTis connecting things to networks by using communication technologies, toimplement an intelligent network for interconnection between persons andmachines and between things.

In response to the various terminal devices described above beinglocated in a vehicle (for example, placed in the vehicle or installed inthe vehicle), the terminal devices are all considered as vehicle-mountedterminal devices. The vehicle-mounted terminal devices are also referredto as, for example, on board units (on-board unit, OBU).

In embodiments disclosed herein, the terminal device further include arelay (relay). Alternatively, it is understood as that any device thatcan perform data communication with a base station is considered as aterminal device.

An access network device in embodiments disclosed herein is a deviceconfigured to communicate with a terminal device, a base station, anaccess point, or a network device, or refer to a device thatcommunicates with a wireless terminal over an air interface in an accessnetwork by using one or more sectors. The network device is configuredto mutually convert a received over-the-air frame and an IP packet andserve as a router between the wireless terminal and a remaining portionof the access network, where the remaining portion of the access networkincludes an internet protocol (IP) network. The network device isfurther coordinate attribute management of the air interface. Forexample, the access network device is a base transceiver station (BaseTransceiver Station, BTS) in a global system for mobile communication(Global System of Mobile communication, GSM) or code division multipleaccess (Code Division Multiple Access, CDMA), a NodeB (NodeB, NB) inwideband code division multiple access (Wideband Code Division MultipleAccess, WCDMA), is an evolved NodeB (evolved NodeB, eNB or eNodeB) in anLTE system, or is a radio controller in a cloud radio access network(cloud radio access network, CRAN) scenario. Alternatively, the accessdevice is a relay station, an access point, a vehicle-mounted device, awearable device, an access device in a 5G network, a network device in afuture evolved PLMN network, or the like, is an access point (accesspoint, AP) in a WLAN, or may be a gNB in a new radio (new radio, NR)system. This is not limited in embodiments disclosed herein. In a 5Gsystem, there are one or more transmission reception points(Transmission Reception Point, TRP) in one base station. All TRPs belongto a same cell. The measurement reporting method in embodimentsdisclosed herein are used for each TRP and each terminal. In anotherscenario, the network device may be further divided into a control unit(Control Unit, CU) and a data unit (Data Unit, DU). One CU correspondsto a plurality of DUs. The measurement reporting method in embodimentsdisclosed herein are used for each DU and each terminal. A differencebetween a CU-DU split scenario and a multi-TRP scenario lies in: The TRPis a radio frequency unit or an antenna device while the DU canimplement a protocol stack function, for example, a physical layerfunction.

In addition, in embodiments disclosed herein, the access network deviceis a device in the access network (radio access network, RAN), in otherwords, is a RAN node that connects the terminal device to a wirelessnetwork. For example, by way of example but not limitation, the accessnetwork device is a gNB, a transmission reception point (transmissionreception point, TRP), an evolved NodeB (evolved NodeB, eNB), a radionetwork controller (radio network controller, RNC), a NodeB (NodeB, NB),a base station controller (base station controller, BSC), a basetransceiver station (base transceiver station, BTS), a home base station(for example, a home evolved NodeB or a home NodeB, HNB), a base bandunit (base band unit, BBU), or a wireless fidelity (wireless fidelity,Wi-Fi) access point (access point, AP).

The access network device serves a cell. The terminal devicecommunicates with the access network device by using a transmissionresource (for example, a frequency domain resource or a spectrumresource) used for the cell. The cell is a cell corresponding to theaccess network device (for example, a base station). The cell belongs toa macro base station, or belongs to a base station corresponding to asmall cell (small cell). The small cell herein includes a metro cell(metro cell), a micro cell (micro cell), a pico cell (pico cell), afemto cell (femto cell), or the like. The small cells have features ofsmall coverage and a low transmit power, and are suitable for providinga high-rate data transmission service.

Unicast (unicast): a point-to-point communication technology, to bespecific, single-point communication between a network device and aterminal device. The network device separately sends data to eachterminal device. The unicast is also referred to as a unicasttransmission mode or a unicast transmission technology.

Sending performed in the unicast transmission mode means: In response tosending a transport block (transport block, TB) corresponding to aprotocol data unit (protocol data unit, PDU), a sending apparatusscrambles, by using a cell radio network temporary identifier (cellnetwork temporary identifier, C-RNTI), the PDU or downlink controlinformation (downlink control information, DCI) corresponding to thePDU, and a receiving apparatus receives the same PDU based on theC-RNTI. Alternatively, transmitting a PDU in the unicast mode means: ThePDU is transmitted on a radio bearer established for unicasttransmission or on a channel specially designed for the unicast.

Receiving performed in the unicast transmission mode means: In responseto sending being performed in the unicast mode, the receiving apparatusreceives the PDU based on the C-RNTI, or the receiving apparatusreceives the PDU on the radio bearer established for the unicasttransmission or on the channel used for the unicast transmission.

Multicast (multicast): a point-to-multipoint communication technology,which is also referred to as a multicast transmission mode or amulticast transmission technology, and is for serving a multimediabroadcast multicast service. The multicast is also referred to asgroupcast, and is also referred to as a broadcast technology in somegeneralized scenarios. However, the multicast is different from aconventional broadcast technology. In response to the multicasttransmission mode being used, a plurality of terminal devicessimultaneously receive a same piece of data in a process in which anetwork device (for example, a base station) sends the data. Currently,multicast transmission technologies are classified into two types: amultimedia broadcast multicast service single frequency network(multimedia broadcast multicast service single frequency network, MBSFN)service and a single-cell point-to-multipoint (single cell point tomultipoint, SC-PTM) service. In addition, another multicast transmissiontechnology is also discussed. This is not limited in the presentinvention.

Sending performed in the multicast transmission mode means: In responseto sending a transport block (transport block, TB) corresponding to aprotocol data unit (protocol data unit, PDU), a sending apparatusscrambles, by using a group radio network temporary identifier (groupradio network temporary identifier, G-RNTI), the PDU or downlink controlinformation (downlink control information, DCI) corresponding to thePDU, and one or more receiving apparatuses receive the same PDU based onthe same G-RNTI. Alternatively, transmitting a PDU in the multicast modemeans: A plurality of receiving apparatuses are notified of a locationof a same PDU in a semi-persistent manner, and the plurality ofreceiving apparatuses simultaneously receive the PDU. Alternatively,transmitting a PDU in the multicast mode means: The PDU is transmittedon a radio bearer established for multicast transmission or on a channelspecially designed for the multicast.

Receiving performed in the multicast transmission mode means: Inresponse to sending being performed by a peer side in the multicastmode, one of the plurality of receiving apparatuses receives the PDUbased on the G-RNTI, or one of the plurality of receiving apparatusesreceives the PDU on the radio bearer established for the multicasttransmission or on the channel used for the multicast transmission.

Broadcast: a point-to-multipoint communication technology. Differentfrom multicast, the technology related to the broadcast is: A sendingapparatus sends a TB corresponding to a PDU on a broadcast channel, andall receiving apparatuses receive the PDU on the broadcast channel.Different from a multicast technology, in conventional broadcasttransmission, the foregoing scrambling manner using the G-RNTI is notused for the broadcast channel.

Handover (handover, HO): An ongoing call is handed over from a wirelesschannel to another wireless channel, to ensure that communication is notinterrupted. In a wireless communication system, each cell covers alimited range. Therefore, in response to a terminal device moving from acurrent serving cell to a neighboring cell, to ensure servicecontinuity, a network side hands over a service to the neighboring cell,so that a communication process is not interrupted. The handover is aprocess in which a link carrying communication data is handed over froma cell (or a base station) to another cell (or another base station) ina communication process, to ensure that communication is notinterrupted.

Protocol stack (Protocol Stack): A network device and a terminal devicehave specific protocol layer structures that are used for mutualcommunication. For example, a control plane protocol layer structureincludes a radio resource control (radio resource control, RRC) layer, apacket data convergence protocol (Packet Data Convergence Protocol,PDCP) layer, a radio link control (radio link control, RLC) layer, amedia access control (media access control, MAC) layer, and a physicallayer. A user plane protocol layer structure includes a PDCP layer, anRLC layer, a MAC layer, a physical layer, and the like. The physicallayer is located at the lowest layer (layer 1), the MAC layer, the RLClayer, and the PDCP layer belong to the second layer (layer 2), and theRRC layer belongs to the third layer (layer 3). In an implementation, aservice data adaptation protocol (service data adaptation protocol,SDAP) layer is further included above the PDCP layer. In addition, atransport layer, for example, a transmission control protocol/internetprotocol (Transmission Control Protocol/Internet Protocol, TCP/IP)layer, and an application layer, further exists above the SDAP layer.

Functions of the protocol layers are implemented by one node, orimplemented by a plurality of nodes. For example, in an evolvedstructure, a radio access network device includes a centralized unit(centralized unit, CU) and a distributed unit (distributed unit, DU). Aplurality of DUs are centrally controlled by one CU. The CU and the DUare obtained through division based on a protocol layer of a wirelessnetwork. For example, functions of the PDCP layer and a layer above thePDCP layer are set on the CU, and functions of a protocol layer belowthe PDCP layer, the RLC layer, the MAC layer, and the like are set onthe DU.

Division based on the protocol layer is an example, and division isalternatively be performed based on another protocol layer. For example,division is performed based on the RLC layer. Functions of the RLC layerand a layer above the RLC layer are set on the CU, and a function of aprotocol layer below the RLC layer is set on the DU. Alternatively,division is performed at a protocol layer. For example, a part offunctions of the RLC layer and a function of a protocol layer above theRLC layer are set on the CU, and a remaining function of the RLC layerand a function of a protocol layer below the RLC layer are set on theDU. In addition, division is alternatively performed in anotherembodiment. For example, division is performed based on a latency. Afunction whose processing time satisfies a latency requirement is set onthe DU, and a function whose processing time does not satisfy thelatency requirement is set on the CU.

Radio bearer (Radio Bearer): Generally, the radio bearer is understoodas a transmission path or treatment (treatment) used in response to adata packet or signaling being transmitted over an air interface. Radiobearers include a data radio bearer and a signaling radio bearer. Theradio bearer is established and configured by using RRC signaling of anetwork device. A configuration of the radio bearer includesconfigurations of protocol layers. Protocol layer entities of thenetwork device and a terminal device send, receive, or process the datapacket or the signaling on the radio bearer based on the configuration.Technically, the radio bearer is understood as a transmission channel.Regardless of a terminal device side or a network device side, eachradio bearer includes one PDCP entity and at least one RLC entity toprocess the data packet transmitted on the radio bearer. In addition toestablishing the radio bearer, the network device further adds,modifies, or deletes (release) the radio bearer by using RRC signaling.

A multimedia broadcast multicast service is used for apoint-to-multipoint unidirectional multimedia service. For example, amultimedia broadcast service is sent to a user in a cell on a commonchannel over an air interface, or a multicast service subscribed to by auser in a cell is sent to the user in a multicast mode, so that airinterface resources are reduced.

The following describes a scenario in at least one embodiment disclosedherein. FIG. 1 is a schematic diagram of an application scenario 100according to at least one embodiment disclosed herein. In FIG. 1 , anaccess network device 110, a terminal device 120, a terminal device 130,a terminal device 140, a terminal device 150, a terminal device 160, anda terminal device 170 are included. For example, the access networkdevice 110 works in an evolved universal mobile telecommunication systemterrestrial radio access (evolved UMTS terrestrial radio access, E-UTRA)system, works in an NR system, or works in a next-generationcommunication system or another communication system. The access networkdevice 110 communicates with the terminal device 120 to the terminaldevice 170 through a Uu interface. In the communication system, theterminal device 120 to the terminal device 170 sends uplink data to theaccess network device 110, and the access network device 110 sendsdownlink data to the terminal device 120 to the terminal device 170. Inaddition, a communication system alternatively includes the terminaldevice 150 to the terminal device 170. The access network device 110sends downlink data to the terminal device 120 to the terminal device150, where the access network device 110 sends downlink data to theterminal device 120 and the terminal device 150 in a unicast mode, andthe access network device 110 sends downlink data to the terminal device130 and the terminal device 140 in a multicast mode. The terminal device150 alternatively sends downlink data to the terminal device 160 and theterminal device 170.

The access network device in FIG. 1 is, for example, a base station. Theaccess network device corresponds to different devices in differentsystems. For example, the access network device corresponds to an eNB ina 4G system, and corresponds to an access network device, for example, agNB, in 5G in a 5G system. The technical solutions provided inembodiments disclosed herein are alternatively applied to a futuremobile communication system. Therefore, the access network device inFIG. 1 alternatively corresponds to an access network device in thefuture mobile communication system. In FIG. 1 , an example in which theaccess network device is the base station is used. Actually, for theaccess network device, refer to the foregoing descriptions.

The communication system shown in FIG. 1 further includes more networknodes, for example, another terminal device or access network device.The access network devices or the terminal devices included in thecommunication system shown in FIG. 1 is the foregoing access networkdevices or terminal devices in various forms. These are not shown one byone in the figure in embodiments disclosed herein.

The technical solutions disclosed herein are alternatively applied toanother communication system provided that a transmission direction isindicated in the communication system. In addition, the embodimentsdisclosed herein are not only applicable to a scenario (for example, anSC-PTM scenario) in which one access network device and a plurality ofUEs, but also applicable to a scenario (for example, an MBSFN scenario)in which a plurality of access network devices coordinate tosimultaneously perform data communication with a plurality of UEs and amulticast/broadcast scenario in 5G.

The following describes in detail, with reference to FIG. 2 , acommunication method provided in some embodiments. FIG. 2 is a schematicflowchart of a communication method 200 according to at least embodimentdisclosed herein. The method 200 is applied to the scenario shown inFIG. 1 , or certainly is applied to another communication scenario. Thisis not limited in this embodiment.

In some embodiments disclosed herein, the method is described by usingan example in which terminal devices, access network devices, and a corenetwork device perform the method. By way of example but not limitation,the method is alternatively performed by chips, chip systems,processors, or the like used in terminal devices, access networkdevices, and a core network device.

As shown in FIG. 2 , the method 200 shown in FIG. 2 includes S201 toS210. The following describes in detail the steps in the method 200 withreference to FIG. 2 .

S201: A data server sends at least one data packet of a first service tothe core network device.

Optionally, the data server includes progress indication information ofthe first service in the at least one data packet of the first servicein response to sending the at least one data packet to the core networkdevice. The progress indication information indicates a sequence of acurrent data packet in the at least one data packet of the firstservice. The progress indication information of the first service is asequence number of the first service. The progress indicationinformation is carried in a data packet, for example, in a header of thedata packet. Alternatively, the indication information is separatelysent, which is independent from the sending of the data packet.

Optionally, before S201, the data server receives request informationsent by the core network device. The request information requests thedata server to include the progress indication information of the firstservice in the at least one data packet of the first service in responseto the data server sending the at least one data packet to the corenetwork device. In response to receiving the request information sent bythe core network device and sending the at least one data packet of thefirst service to the core network device, the data server includes theprogress indication information of the first service in each datapacket.

Optionally, the first service is an MBMS service.

S202: The core network device receives the at least one data packet thatis of the first service and that is sent by the data server.

Specifically, in response to receiving the at least one data packet thatis of the first service and that is sent by the data server, the corenetwork device determines an access network device to receive the firstservice, thereby separately sending the at least one data packet todifferent access network devices.

S203: The core network device sends a first data packet and firstindication information to a first access network device, where the firstindication information indicates a sequence of the first data packet inthe at least one data packet sent by the core network device.

In some embodiments disclosed herein, S201 and S202 are optional steps,and S203 unnecessarily depends on S201 and S202. Specifically, a datapacket received by the core network device is received from anotherplace or generated by the core network device. Optionally, the corenetwork device alternatively receives the progress indicationinformation from another place, and determine positions of data packetsbased on the progress indication information. In addition, how a corenetwork device sends the data packets to the different access networkdevices is not limited.

S204: The core network device sends a second data packet and secondindication information to a second access network device, where thefirst indication information indicates a sequence sequence of the seconddata packet in the at least one data packet sent by the core networkdevice. Data in the first data packet is the same as or different fromdata in the second data packet. This is not limited. In response to datain a data packet received by the first access network device being thesame as data in a data packet received by the second access networkdevice, the first indication information is the same as the secondindication information.

For example, in response to the core network device sending five datapackets whose core network sequence numbers are 1 to 5 to the firstaccess network device, and sends five data packets whose core networksequence numbers are 5 to 9 to the second access network device, contentand a size of the last data packet in the five data packets received bythe first access network device are the same as those of the first datapacket in the five data packets received by the second access networkdevice, and indication information corresponding to the two data packetsis the same.

Specifically, in response to the core network device sending the atleast one data packet of the first service to the access network device,the at least one data packet carries the first indication information,so that the access network device can learn of sending progress of thefirst service. The first indication information is implemented bysetting a core network sequence number for the data packet. In responseto sending, to the different access network devices, the data packetsreceived from the data server, the core network device enables same datapackets (where carried content or carried payloads are the same) tocarry same core network sequence numbers, namely, same first indicationinformation, where the first indication information identifies asequence of the data packet in at least one sent data packet.

Optionally, the first indication information includes at least one ofthe following information: a general packet radio service tunnelingprotocol-user plane sequence number (GPRS Tunneling Protocol-U SequenceNumber, GTP-U SN) and the first service sequence number. The firstservice sequence number is set by the core network device or the dataserver, the first data packet is a data packet of the first service, andthe at least one data packet is a data packet of the first service.

The following briefly describes the first service sequence number byusing the GTP-U sequence number as an example. Currently, during datatransmission between the core network device and the access networkdevice, the core network device establishes different PDU sessions orGTP tunnels with the different access network devices for separateoperation. Therefore, even if the core network device receives same datapackets from the data server, the core network device sets differentGTP-U SN in response to sending the same data packets to the differentaccess network devices. However, in some embodiments, the core networkdevice sets, in response to sending same data packets received by thecore network device from the data server or generated by the corenetwork device to the different access network devices, same GTP-U SNfor the data packets. In an embodiment, a GTP-U SN is set for each datapacket based on indication information of the data server. In this way,because the GTP-U SN is associated with content of the data packet, thedifferent access network devices determine service transmission progressbased on the GTP-U SN.

Optionally, in response to the data server sending the at least one datapacket of the first service to the core network device, in response tothe at least one data packet carrying at least one first servicesequence number respectively corresponding to the at least one datapacket, the core network device sends the first indication informationto the access network device based on the first service sequence number.The first indication information is the first service sequence numbercarried in the at least one data packet. In response to the data serversending the at least one data packet of the first service to the corenetwork device, in response to the at least one data packet not carryingthe first service sequence number, the core network device resets afirst service sequence number of the at least one data packet based on asequence of receiving the at least one data packet. For example, inresponse to the core network device receiving a data packet 1, a datapacket 2, and a data packet 3 from the data server, the core networkdevice sets a first service sequence number 1 for the data packet 1, seta first service sequence number 2 for the data packet 2, and set a firstservice sequence number 3 for the data packet 3.

S205: The first access network device receives the first data packet andthe first indication information from the core network device.

A specific implementation in which S205 depends on the foregoing stepsis not limited in some embodiments disclosed herein provided that thefirst data packet and the first indication information are received fromthe core network device.

S206: The first access network device determines a first sequence numberof a first protocol layer of the first data packet based on the firstindication information.

Optionally, the first protocol layer includes at least one of thefollowing protocol layers: a service data adaptation protocol SDAPlayer, a packet data convergence protocol PDCP layer, and a radio linkcontrol layer RLC layer.

The first protocol layer is an upper-layer protocol layer on a radioaccess network side, the first protocol layer is also referred to as alayer 2 protocol layer, and SDAP, PDCP, RLC, and MAC all belong to layer2 protocols. In addition, in a subsequent technology, a new protocollayer may be introduced for a new function. Therefore, in someembodiments disclosed herien, the first protocol layer is not limited toan existing protocol layer, or is a newly defined protocol layer.

Specifically, after receiving the first data packet, the first accessnetwork device determines the first sequence number of the firstprotocol layer of the first data packet based on the first indicationinformation. The first sequence number of the first protocol layer isused by the first protocol layer to process the first data packet, forexample, perform sorting or duplicate detection.

Optionally, in response to the first access network device establishinga first protocol layer entity for multicast transmission, are-establishment (re-establishment) process occurs on the first protocollayer entity that has been established and that is for the multicasttransmission, or a data recovery (data recovery) process of the firstprotocol layer entity occurs, the first protocol layer entity of thefirst access network device determines a start sequence number of thefirst data packet based on the first indication information. A PDCPentity is used as an example. After a PDCP entity for the multicasttransmission is re-established, the access network device receives firstindication information of the first data packet. For example, inresponse to the first indication information being a core networksequence number, a core network sequence number corresponding to thefirst data packet is 5. In some embodiments disclosed herein, the accessnetwork device also sets a PDCP sequence number of the first data packetto 5 instead of 0 from which the PDCP sequence number starts in aconventional technology. Even if the first protocol layer entity isre-established or recovered, it can be ensured that informationcorresponding to a data packet is current actual service progressinformation.

S207: The second access network device receives the second data packetand the first indication information from the core network device.

S208: The second access network device determines a second sequencenumber of a first protocol layer of the second data packet based on thefirst indication information.

In step S206 and step S208, in response to receiving the data packetsand the core network sequence numbers that are sent by the core networkdevice, the first access network device and the second access networkdevice determine the sequence numbers of the received data packets. Tounderstand the step more clearly, the following briefly describes thestep with reference to FIG. 6 . The first access network device receivesa first data packet whose core network sequence number GTP-U SN is 8,and the first access network device determines, based on the GTP-U SN ofthe first data packet, that a PDCP SN of the first data packet is 8. Thesecond access network device receives a data packet whose core networksequence number GTP-U SN is 11, and the second access network devicedetermines, because the GTP-U SN of the second data packet is 11, that aPDCP SN of the second data packet is 11. PDCP is an example of a firstprotocol layer.

The second access network device is alternatively the first accessnetwork device. For descriptions of the second access network device,refer to the foregoing descriptions of the first access network device.Details are not described herein again.

The core network device sends same first services to the first accessnetwork device and the second access network device, and includes samefirst indication information in data packets having same content, sothat the first access network device and the second access networkdevice can determine, based on the same first indication information,same sequence numbers of first protocol layers for the data packetshaving the same content. That is, sequence numbers that are of firstprotocol layers and that are determined by different access networkdevices are the same for data packets having same data. Therefore, in aprocess in which a terminal device is handed over from the first accessnetwork device to the second access network device, the second accessnetwork device learns of first service progress of the first accessnetwork device based on SN status forwarding and data forwarding stepsin an existing handover procedure, without introducing additionalprogress information between the two access network devices.

Some embodiments disclosed herein involve a plurality of sequencenumbers. Sequence numbers of protocol layers of the data server, thecore network device, the access network device, and the terminal deviceis set for the protocol layers. For example, a core network sequencenumber is a sequence number set by the core network device for a datapacket, and a PDCP sequence number is a sequence number set by a PDCPlayer of the access network device or the terminal device for the datapacket. Different sequence numbers have different functions in differentpackets of a same data packet, and are visible only to a correspondingdevice or protocol layer. In addition, the “sequence number” is ageneral term for all sequence numbers, and is not limited to a specificsequence number. A specific sequence number is specifically determinedbased on a scenario. For example, a sequence number of a PDCP layer is aPDCP sequence number.

In response to a data packet being sent from the core network device tothe access network device and then to the terminal device, the datapacket is processed (where for example, a header of the data packet isadded) at many different protocol layers. The processing is used fortransmission. After the processing, a size or a form of the data packetchanges. However, provided that content of a payload of the data packetdoes not change, the data packet is referred to as a same data packet,for example, the first data packet.

S209: The first access network device sends the first data packet to afirst terminal device.

Optionally, the first access network device sends second indicationinformation to the first terminal device. The second indicationinformation indicates a sequence number of the first data packet that isof the first service and that is sent by the first access network deviceto the first terminal device after a first protocol entity of the firstterminal device is established, the first protocol entity isre-established, or data recovery occurs on the first protocol entity.

In an embodiment, before the first terminal device starts to receive thefirst service, in response to the first protocol entity beingestablished, the first terminal device first obtains, from the firstaccess network device, configuration information for receiving the firstprotocol entity. The first access network device includes the secondindication information in the configuration information, where thesecond indication information indicates a sequence number (for example,a PDCP SN) of the first data packet that is of the first service andthat is sent by the first access network device. In this way, theterminal device learns of the sequence number of the first data packetthat should be received. In response to a sequence number of the firstreceived data packet being greater than the sequence number indicated bythe indication information, it indicates that a data packet is lost. Theterminal device determines a lost data packet and request the accessnetwork device to retransmit the lost data packet.

In addition, in response to a re-establishment process or a datarecovery process occurs on the first protocol entity used by theterminal device to transmit the first service, the access network devicealso sends the second indication information to the first terminaldevice, where the second indication information indicates the sequencenumber (for example, the PDCP SN) of the first data packet that is ofthe first service and that is sent by the first access network device.Therefore, a data packet loss caused by inconsistent understanding ofthe first data packet by the first terminal device and the first accessnetwork device can be avoided.

S210: The second access network device sends the second data packet to asecond terminal device.

Optionally, the second access network device sends the second indicationinformation to the second terminal device. For specific descriptions,refer to related descriptions in S209. Details are not described hereinagain.

According to the communication method 200 provided in some embodiments,in the process in which the terminal device is handed over from thefirst access network device to the second access network device, thesecond access network device learns of the first service progress of thefirst access network device based on the SN status forwarding and dataforwarding steps in the existing handover procedure, without introducingthe additional progress exchange information between the two accessnetwork devices. In this way, a case in which a redundant data packet isreceived by the terminal or service data is interrupted becausemulticast service progress of the different access network devices isinconsistent can be avoided.

To better understand beneficial effects of the method provided in someembodiments, the following briefly describes a procedure of handing overa terminal device between access network devices (for example, basestations) in a conventional technology. The procedure of the handoverbetween the base stations (gNBs) is shown in FIG. 3 . FIG. 3 is aschematic flowchart of a method 300 of handing over the terminal devicebetween the access network devices in the conventional technology. Thehandover is initiated by a source gNB. The source gNB (Source gNB, SgNB)determines to hand over a UE based on a measurement report reported bythe UE, and initiates a handover request to a target gNB (Target gNB,TgNB). After the SgNB obtains a positive handover acknowledgment fromthe TgNB, the SgNB sends a handover command to the UE. After the UEreceives the handover command, the UE stops uplink or downlink datatransmission with the SgNB, starts to synchronize with the TgNB, andinitiates a random access process. In response to sending the handovercommand to the UE, the SgNB stops performing uplink or downlink datatransmission with the UE, and sends data stored in the SgNB to the TgNB.After successfully accessing the TgNB, the UE starts to transmit uplinkor downlink data with the TgNB. The method 300 shown in FIG. 3 includesS301 to S308. The following briefly describes steps in the method 300with reference to FIG. 3 .

S301: In a handover preparation phase, the UE in an RRC connected statesends the “measurement report” (Measurement Report) according to ameasurement reporting trigger criterion configured by the gNB.

S302: The source gNB determines the target gNB for the UE based on themeasurement report of the UE and a radio resource management algorithmRRM algorithm in response to the UE meeting a handover condition, andsends UE context (UE Context) information to the target gNB via thehandover request.

S303: The target gNB makes preparations for the UE to be handed over tothe target gNB, allocates a cell identity parameter C-RNTI and anotherparameter to the UE, and returns the C-RNTI and the another parameter tothe source gNB via a handover request acknowledgment message. Afterreceiving the handover request acknowledgment message, the source gNBprepares to forward packet data to the target gNB.

S304: The SgNB sends the “handover command” (Handover Command) to the UE(where the handover command includes the following information: a newC-RNTI, a SIB of the target gNB, and configuration information of the UEsuch as configurations of MAC, RLC, and PDCP layers). After receivingthe handover command, the UE stops the uplink or downlink datatransmission with the source gNB, and synchronizes with the target gNB.

In some embodiments disclosed herein, the source gNB forwards, to thetarget gNB, buffered uplink data sent by the UE and buffered downlinkdata sent by a UPF.

S305: The source gNB sends SN status information and forwards data (adashed-line step) to the target gNB.

S306: After disconnecting data transmission with the source gNB, the UEstarts a downlink synchronization process with the target gNB, and theninitiates the random access process to obtain uplink timing and uplinkresource allocation. The target gNB sends a tracking area TA to the UEand indicates, to the UE, a resource allocated to the UE. Theinformation is used by the UE to send an RRC connection reconfigurationcomplete message to the target gNB, to indicate handover completion.

S307: The UE sends “handover acknowledgment” information to the targetgNB, to indicate the handover completion.

S308: The target gNB indicates the handover completion to the sourcegNB, so that the source gNB releases the UE context information.

In addition, the target gNB notifies a core network node to updateinformation about the target gNB to which data is forwarded, so that thecore network can send data of the UE to the target gNB.

In a conventional technology, in some multicast scenarios, a UE receivesa multicast (groupcast) service from a base station, moves at a moment,and performs a handover procedure to be handed over to another basestation to receive a multicast service. In response to progress of themulticast services of the two base stations being inconsistent, theexisting handover procedure causes the UE to receive a redundant datapacket or cause data interruption of the UE. FIG. 4 is a schematicdiagram of a multicast service handover scenario 400. In FIG. 4 , a corenetwork device 410, an access network device 420, an access networkdevice 430, a terminal device 440, and a terminal device 450 areincluded. The access network device 420 and the access network device430 receive multicast service data sent by the core network device 410,and send the multicast service data to terminal devices within coverageof the access network device 420 and the access network device 430. Theterminal device 450 is handed over from the access network device 420 tothe access network device 430. Progress of multicast services of theaccess network device 420 and the access network device 430 isinconsistent. An existing handover procedure causes the terminal device450 to receive a redundant data packet or cause data interruption of theterminal device 450.

To resolve the problem, some embodiments provide a communication method500. The following describes in detail, with reference to FIG. 5 , acommunication method provided in some embodiments. FIG. 5 is a schematicflowchart of the communication method 500 according to at least oneembodiment disclosed herein. The method 500 is applied to the scenarioshown in FIG. 1 , or certainly is applied to another communicationscenario. This is not limited in this embodiment. In the method 500, afirst terminal device connected to a first access network device ishanded over from the first access network device to a second accessnetwork device, and both the first access network device and the secondaccess network device perform a first service.

Before and after the handover of the first terminal device, the firstterminal device processes, by using a same protocol entity, data packetsreceived from the first access network device and the second accessnetwork device before and after the handover, for example, performssorting or duplicate detection.

In some embodiments, the method is described by using an example inwhich the terminal device and the access network devices perform themethod. By way of example but not limitation, the method isalternatively performed by chips, chip systems, processors, or the likeused in the terminal device and the access network devices.

As shown in FIG. 5 , the method 500 shown in FIG. 5 includes S501 toS505. The following describes in detail the steps in the method 500 withreference to FIG. 5 .

S501: The first access network device forwards a data packet to thesecond access network device, where the data packet sent by the firstaccess network device is a data packet of the first service.

S502: The second access network device receives the data packet sent bythe first access network device.

Specifically, in a handover process, the first access network deviceforwards, to the second access network device, data that is sent by acore network device and that is not successfully sent to the firstterminal device. This is a data forwarding process. Both sequencenumbers of first protocol layers of the two access network devices aredetermined based on first indication information sent by the corenetwork device. Therefore, for data packets having same content,sequence numbers that are of first protocol layers and that aredetermined by the two access network devices are the same. Therefore,after receiving the data packet forwarded by the first access networkdevice, the second access network device can learn of sending progressof the first service in the first access network device based on asequence number of a first protocol layer of the data packet, and canuse a corresponding sending policy to ensure service continuity of thefirst terminal device.

S503: The second access network device determines, based on a secondsequence number of a first protocol layer of a data packet that is beingsent to the first terminal device and a first sequence number of a firstprotocol layer of the data packet received from the first access networkdevice, whether to send third indication information to the first accessnetwork device, where the third indication information indicates thefirst access network device to stop forwarding a data packet to thesecond access network device.

Optionally, in response to the second sequence number of the firstprotocol layer of the data packet that is being sent by the secondaccess network device to the first terminal device being greater than orequal to the first sequence number of the first protocol layer of thedata packet sent by the first access network device, the second accessnetwork device sends the third indication information to the firstaccess network device.

Optionally, in response to the second sequence number of the firstprotocol layer of the data packet that is being sent by the secondaccess network device to the first terminal device being N, and thefirst sequence number of the first protocol layer of the data packetsent by the first access network device is N-1, the second accessnetwork device sends the third indication information to the firstaccess network device.

Specifically, after the terminal device is successfully handed over, thesecond access network device starts to send a data packet of the firstservice to the terminal device, and the first access network deviceforwards, to the second access network device, a data packet that is ofthe first service and that is not successfully received by the terminalfrom the first access network device. In response to a sequence numberof the data packet received by the second access network device from thefirst access network device being greater than or equal to a sequencenumber of the data packet sent to the terminal device, the second accessnetwork device indicates to stop data forwarding. For the first service,it is assumed that sending progress of the second access network deviceis fast. FIG. 6 is a schematic flowchart of the data forwarding of thecommunication method according to some embodiments disclosed herein. Auser plane function receives data packets of a first service that aresent by a data server. In response to the data server sending the datapackets of the first service, the data server includes indicationinformation such as service sequence numbers in the data packets. Theuser plane function separately sends the received data packets of thefirst service to the first access network device and the second accessnetwork device. However, progress of sending the data packets by theuser plane function to the first access network device and the secondaccess network device is inconsistent. A largest sequence number of datapackets of the first service that have been sent by the first accessnetwork device is SN=8, and a largest sequence number of data packets ofthe first service that have been sent by the second access networkdevice is SN=11. In some embodiments disclosed herein, after the firstterminal device is handed over to the second access network device, inresponse to the first terminal device receiving the first service basedon the sending progress of the second access network device, datapackets whose SNs are 9 and 10 are lost. Therefore, the first accessnetwork device forwards the data packets whose SNs are 9 and 10 to thesecond access network device. In response to progress of the datapackets forwarded by the first access network device catching up withthe sending progress of the second access network device, that is, inresponse to a sequence number of a data packet received by the secondaccess network device from the first access network device being greaterthan or equal to an SN of the first data packet that is of the firstservice and that is sent by the second access network device after theterminal device is successfully handed over to the second access networkdevice, the second access network device sends stop indicationinformation to the first access network device, to indicate that thedata forwarding ends.

In an optional implementation, the third indication information includesidentification information of the first service.

S504: The first access network device receives the third indicationinformation from the second access network device.

S505: The first access network device stops, based on the thirdindication information, forwarding the data packet to the second accessnetwork device.

Specifically, after receiving the indication information, the firstaccess network device stops the data forwarding. The first accessnetwork device keeps performing data forwarding before receiving thestop indication information of the target base station.

Therefore, in the handover process of the first terminal device, thesecond access network device determines whether the data forwarding ofthe first access network device is stopped, and sends the dataforwarding stop indication information to the first access networkdevice, so that multicast service receiving continuity of the terminaldevice in the handover process is ensured, and a packet loss orredundant transmission is avoided.

Optionally, before step S501, the method 500 includes the followingsteps.

The second access network device receives status report information thatis of a data packet and that is sent by the first terminal device, wherethe status report information of the data packet indicates, to thesecond access network device, a data packet that is of the first serviceand that has been successfully received by the first terminal device anda data packet that has not been successfully received by the firstterminal device.

The second access network device sends fourth indication information tothe first access network device based on the status report information,where the fourth indication information indicates a sequence number ofthe first data packet forwarded by the first access network device tothe second access network device, and the first data packet is a datapacket that the first access network device starts to forward to thesecond access network device or a data packet with a smallest sequencenumber in all forwarded data packets in a data forwarding process.

The first access network device receives the fourth indicationinformation sent by the second access network device.

The first access network device forwards a data packet to the secondaccess network device based on the fourth indication information.

Specifically, the first terminal device sends the status reportinformation of the data packet to the second access network device afterthe handover, where the status report information indicates, to thesecond access network device, data packets successfully received by thefirst terminal device and data packets unsuccessfully received by thefirst terminal device. After receiving the status report information,the second access network device sends the fourth indication informationto the first access network device, where the fourth indicationinformation indicates a sequence number of a first protocol layer of thefirst data packet that is not received by the first terminal device,namely, a start data packet in data forwarding by the first accessnetwork device. In this way, the first terminal device can be preventedfrom receiving a redundant data packet. To be specific, the followingcase can be avoided: A data packet sent by the first access networkdevice is successfully received by the first terminal device, but isstill forwarded by the first access network device to the second accessnetwork device, and then sent by the second access network device to thefirst terminal device.

Some embodiments disclosed herein provide a communication method 600.The following describes in detail, with reference to FIG. 7 , acommunication method provided in some embodiments. FIG. 7 is a schematicflowchart of the communication method 600 according to some embodimentsdisclosed herein. The method 600 is applied to the scenario shown inFIG. 1 , or certainly is applied to another communication scenario. Thisis not limited in this embodiment. In the method 600, in a process inwhich a first terminal device connected to a first access network deviceis handed over from the first access network device to a second accessnetwork device, the terminal device keeps connected to both the firstaccess network device and the second access network device. In this way,the first access network device and the second access network devicesimultaneously send first services to the terminal device. The firstaccess network device continues to send a data packet that is notsuccessfully received by the terminal device before the handover. Inaddition, the terminal device receives a data packet of the firstservice from the second access network device. In response to a sequencenumber of the data packet received from the first access network devicebeing consecutive to a sequence number of the data packet received fromthe second access network device (where for example, a data packet witha largest SN 9 is received from the first access network device, and adata packet with a smallest SN 10 is received from the second accessnetwork device), the first access network device stops sending a datapacket to the terminal device, and disconnects from the terminal device.

In some embodiments, the method is described by using an example inwhich the terminal device and the access network devices perform themethod. By way of example but not limitation, the method isalternatively performed by chips, chip systems, processors, or the likeused in the terminal device and the access network devices.

As shown in FIG. 7 , the method 600 shown in FIG. 7 includes S601 toS603. The following describes in detail the steps in the method 600 withreference to FIG. 7 .

S601: The second access network device sends fifth indicationinformation to the first access network device, where the fifthindication information includes a first sequence number N, and the firstsequence number indicates a sequence number of the first data packetthat is of the first service and that is sent by the second accessnetwork device to the first terminal device after the first terminaldevice is successfully handed over from the first access network deviceto the second access network device.

S602: The first access network device receives the fifth indicationinformation sent by the second access network device.

S603: In response to a sequence number of a data packet successfullysent by the first access network device to the terminal device beingN-1, the first access network device stops sending a data packet to theterminal device.

Therefore, in a handover process, the first access network devicedetermines, based on the SN indicated by the second access networkdevice, when to stop a connection to the terminal device, so thatmulticast service receiving continuity of the terminal device in thehandover process is ensured, and a packet loss or redundant transmissionis avoided.

Specifically, in the handover process, the first terminal devicereceives data packets of the first services from both the first accessnetwork device and the second access network device. The first accessnetwork device does not forward the data packet of the first service tothe second access network device. That is, a data forwarding process isnot used. For example, in FIG. 5 , data forwarding is not performed onthe data packets whose SNs are 9 and 10, and the data packets aredirectly sent to the first terminal device by the first access networkdevice. After the first terminal device is successfully handed over tothe second access network device, the second access network devicesends, to the first access network device, the SN (for example, 11) ofthe first data packet that is of the first service and that is sent tothe terminal device. The first access network device determines, basedon the SN of the first data packet, when to stop sending data to thefirst terminal device. In response to the sequence number of a firstprotocol layer of the data packet successfully sent by the first accessnetwork device to the terminal device being N-1, the first accessnetwork device stops sending the data packet to the first terminaldevice. For example, in FIG. 5 , after sending the data packet withnumber 11-1=10, the first access network device disconnects from thefirst terminal device.

Optionally, the first access network device sends stop indicationinformation to the second access network device, to indicate the firstaccess network device to disconnect from the first terminal device.

Optionally, in response to the terminal device being successfully handedover to the second access network device, the second access networkdevice sends, to the first access network device, information indicatingthat the first terminal device is successfully handed over. After thefirst access network device receives the information indicating that thefirst terminal device is successfully handed over, the first accessnetwork device sends, to the second access network device, a firstsequence number of a first protocol layer newly sent to the firstterminal device, the second access network device determines, based onthe first sequence number of the first protocol layer and a secondsequence number of the first protocol layer, whether the first accessnetwork device stops sending the data packet of the first service to thefirst terminal device, where the second sequence number of the firstprotocol layer is a sequence number of a first protocol layer of thefirst data packet received by the first terminal device from the secondaccess network device after the first terminal device is handed overfrom the first access network device to the second access networkdevice. In response to the first sequence number of the first protocollayer being greater than the second sequence number of the firstprotocol layer, the second access network device sends indicationinformation to the first access network device, to indicate the firstaccess network device to disconnect from the first terminal device.

Optionally, the second access network device sends fifth indicationinformation to the first access network device. The fifth indicationinformation includes a first sequence number N-1, and the first sequencenumber indicates the first access network device to stop, in response tothe sequence number of the first protocol layer of the data packetsuccessfully sent by the first access network device to the terminaldevice being N-1, sending the data packet to the terminal device.

Therefore, the first access network device no longer performscalculation, and directly stops sending the data packet after a datapacket whose first sequence number is N-1 is sent.

The foregoing describes in detail, with reference to FIG. 1 to FIG. 7 ,the methods for measuring a communication parameter of a multi-SIMterminal device according to embodiments disclosed herein. The followingdescribes in detail communication apparatus in embodiments disclosedherein with reference to FIG. 8 to FIG. 10 .

FIG. 8 is a schematic block diagram of a communication apparatus 700according to some embodiments disclosed herein.

In some embodiments, the apparatus 700 is a terminal device, or is achip or a circuit, for example, a chip or a circuit that is disposed inthe terminal device.

In some embodiments, the apparatus 700 is an access network device, oris a chip or a circuit, for example, a chip or a circuit that isdisposed in the access network device.

In some embodiments, the apparatus 700 is a core network device, or is achip or a circuit, for example, a chip or a circuit that is disposed inthe core network device.

In some embodiments, the apparatus 700 includes a processing unit 710(that is, an example of a processor) and a transceiver unit 730. In someembodiments, the processing unit 710 is also referred to as adetermining unit. In some embodiments, the transceiver unit 730 includesa receiving unit and a sending unit.

In some embodiments, the transceiver unit 730 is implemented by using atransceiver, a transceiver-related circuit, or an interface circuit.

In some embodiments, the apparatus further includes a storage unit 720.In a some embodiments, the storage unit 720 is configured to storeinstructions. In an embodiment, the storage unit is alternativelyconfigured to store data or information. The storage unit 720 isimplemented by using a memory.

In some embodiments, the processing unit 710 is configured to executethe instructions stored in the storage unit 720, so that the apparatus700 implements the steps performed by the terminal device in theforegoing methods. Alternatively, the processing unit 710 is configuredto invoke the data in the storage unit 720, so that the apparatus 700implements the steps performed by the terminal device in the foregoingmethods.

In some embodiments, the processing unit 710 is configured to executethe instructions stored in the storage unit 720, so that the apparatus700 implements the steps performed by the access network device in theforegoing methods. Alternatively, the processing unit 710 is configuredto invoke the data in the storage unit 720, so that the apparatus 700implements the steps performed by the access network device in theforegoing methods.

For example, the processing unit 710, the storage unit 720, and thetransceiver unit 730 communicate with each other by using an internalconnection path to transfer a control signal and/or a data signal. Forexample, the storage unit 720 is configured to store a computer program,and the processing unit 710 is configured to invoke the computer programfrom the storage unit 720 and run the computer program, to control thetransceiver unit 730 to receive a signal and/or send a signal, tocomplete the steps of the terminal device or the access network devicein the foregoing methods. The storage unit 720 is integrated into theprocessing unit 710, or is disposed separately from the processing unit710.

Optionally, in response to the apparatus 700 being a communicationdevice (for example, the terminal device or the access network device),the transceiver unit 730 includes a receiver and a transmitter. Thereceiver and the transmitter is a same physical entity or differentphysical entities. In response to the receiver and the transmitter beingthe same physical entity, the receiver and the transmitter arecollectively referred to as a transceiver.

In response to the apparatus 700 being the terminal device or theapparatus is the access network device or the core network device, thetransceiver unit 730 is a sending unit or a transmitter when sendinginformation, and the transceiver unit 730 is a receiving unit or areceiver when receiving information. The transceiver unit is atransceiver. The transceiver, the transmitter, or the receiver is aradio frequency circuit. In response to the apparatus including thestorage unit, the storage unit is configured to store computerinstructions. The processor is communicatively connected to the memory.The processor executes the computer instructions stored in the memory,so that the apparatus can perform the method 200, the method 500, or themethod 600. The processor is a general-purpose central processing unit(CPU), a microprocessor, or an application specific integrated circuit(Application Specific Integrated Circuit, ASIC).

Optionally, in response to the apparatus 700 being the chip or thecircuit, the transceiver unit 730 includes an input interface and anoutput interface.

In response to the apparatus 700 being the chip, the transceiver unit730 is the input interface and/or the output interface, a pin, acircuit, or the like. The processing unit 710 executescomputer-executable instructions stored in the storage unit, so that theapparatus can perform the method 200, the method 500, or the method 600.Optionally, the storage unit is a storage unit in the chip, for example,a register or a buffer, or the storage unit is a storage unit in theterminal but outside the chip, for example, a read-only memory (ReadOnly Memory, ROM), another type of static storage device capable ofstoring static information and instructions, or a random access memory(Random Access Memory, RAM).

In an embodiment, It is considered that a function of the transceiverunit 730 is implemented by using a transceiver circuit or atransceiver-dedicated chip. It is considered that the processing unit710 is implemented by using a dedicated processing chip, a processingcircuit, a processing unit, or a general-purpose chip.

In another embodiment, it is considered that the communication device(for example, the terminal device or the access network device) providedin some embodiments disclosed herein is implemented by using ageneral-purpose computer. That is, program code for implementingfunctions of the processing unit 710 and the transceiver unit 730 isstored in the storage unit 720, and a general-purpose processing unitimplements the functions of the processing unit 710 and the transceiverunit 730 by executing the code in the storage unit 720.

In some embodiments, the apparatus 700 is an access network device,where the access network device is a first access network device; or isa chip or a circuit disposed in the first access network device. Inresponse to the apparatus 700 being the first access network device orthe chip or the circuit disposed in the first access network device, thetransceiver unit 730 is configured to receive a first data packet andfirst indication information from a core network device, where the firstindication information indicates a sequence of the first data packet inat least one data packet; the processing unit 710 is configured todetermine a first sequence number of a first protocol layer of the firstdata packet based on the first indication information; and thetransceiver unit 730 is configured to send the first data packet to aterminal device.

In an embodiment, the first indication information includes at least oneof the following information: a general packet radio service tunnelingprotocol-user plane GTP-U sequence number and a first service sequencenumber, where the first service sequence number is set by the corenetwork device or a data server, the first data packet is a data packetof a first service, and the at least one data packet is a data packet ofthe first service.

In an embodiment, the first protocol layer includes at least one of thefollowing: a service data adaptation protocol SDAP layer, a packet dataconvergence protocol PDCP layer, and a radio link control layer RLClayer.

In an embodiment, the processing unit 710 is further configured todetermine a start sequence number of the first protocol layer of thefirst data packet based on the first indication information in responseto any one of establishment of a first protocol entity, re-establishmentof the first protocol entity, and recovery of the first protocol entityoccurs.

In an embodiment, the transceiver unit 730 is further configured to sendsecond indication information to the terminal device, where the secondindication information indicates a sequence number of the first datapacket that is of the first service and that is sent by the first accessnetwork device to the terminal device after the first protocol entity isestablished, the first protocol entity is re-established, or the firstprotocol entity is recovered.

In an embodiment, the transceiver unit 730 is further configured toreceive third indication information from a second access networkdevice, where the third indication information indicates the firstaccess network device to stop forwarding a data packet to the secondaccess network device. The processing unit 710 is configured to stop,based on the third indication information, forwarding the data packet tothe second access network device.

In an embodiment, the transceiver unit 307 is further configured toreceive fourth indication information sent by the second access networkdevice, where the fourth indication information indicates a sequencenumber of the first data packet forwarded by the first access networkdevice to the second access network device. The processing unit 710 isconfigured to forward a data packet to the second access network devicebased on the fourth indication information.

In an embodiment, the transceiver unit 730 is further configured toreceive fifth indication information sent by a second access networkdevice, where the fifth indication information includes a first sequencenumber N, the fifth indication information includes a second sequencenumber N, and the second sequence number indicates a sequence number ofthe first data packet that is of the first service and that is sent bythe second access network device to the terminal device after handoverof the terminal device is completed. The processing unit 710 isconfigured to determine to stop, in response to a sequence number thatis of a protocol layer and that corresponds to a data packetsuccessfully sent by the first access network device to the terminaldevice being N-1, sending a data packet to the terminal device.

In response to the apparatus 700 being configured in the first accessnetwork device or is the first access network device, the modules or theunits in the apparatus 700 is configured to perform the actions or theprocessing processes performed by the first access network device in theforegoing methods. To avoid repetition, detailed descriptions areomitted herein.

In some embodiments, the apparatus 700 is a terminal device, or a chipor a circuit disposed in the terminal device. In response to theapparatus 700 being the terminal device, or the chip or the circuitdisposed in the terminal device, the transceiver unit 730 is configuredto receive second indication information sent by a first access networkdevice, where the second indication information indicates a sequencenumber of the first data packet that is of a first service and that issent by the first access network device to the terminal device after afirst protocol entity is established, the first protocol entity isre-established, or the first protocol entity is recovered.

In an embodiment, the transceiver unit 730 is further configured to: inresponse to the first protocol entity being re-established or recovered,send request information to the first access network device, where therequest information requests the first access network device to send thesequence number of the first data packet that is of the first serviceand that is sent by the first access network device to the terminaldevice after the first protocol entity is re-established or the firstprotocol entity is recovered.

In an embodiment, the transceiver unit 730 is further configured to sendstatus report information of a data packet to a second access networkdevice, where the status report information of the data packetindicates, to the second access network device, a data packetsuccessfully received by the terminal device and a data packetunsuccessfully received by the terminal device, where the terminaldevice is handed over from the first access network device to the secondaccess network device.

In response to the apparatus 700 being configured in the terminal deviceor being the terminal device, the modules or the units in the apparatus700 are configured to perform the actions or the processing processesperformed by the first terminal device in the foregoing methods. Toavoid repetition, detailed descriptions are omitted herein.

In some embodiments, the apparatus 700 is an access network device,where the access network device is a first access network device; or isa chip or a circuit disposed in the first access network device. Inresponse to the apparatus 700 being the first access network device orthe chip or the circuit disposed in the first access network device, thetransceiver unit 730 is configured to receive a first data packet andfirst indication information from a core network device, where the firstindication information indicates a sequence of the first data packet inat least one data packet; the processing unit 710 is configured todetermine a first sequence number of a first protocol layer of the firstdata packet based on the first indication information; and thetransceiver unit 730 is configured to send the first data packet to aterminal device.

In an embodiment, the first indication information includes at least oneof the following information: a general packet radio service tunnelingprotocol-user plane GTP-U sequence number and a first service sequencenumber, where the first service sequence number is set by the corenetwork device or a data server, the first data packet is a data packetof a first service, and the at least one data packet is a data packet ofthe first service.

In an embodiment, the first protocol layer includes at least one of thefollowing: a service data adaptation protocol SDAP layer, a packet dataconvergence protocol PDCP layer, and a radio link control layer RLClayer.

In an embodiment, the processing unit 710 is further configured todetermine a start sequence number of the first protocol layer of thefirst data packet based on the first indication information in responseto any one of establishment of a first protocol entity, re-establishmentof the first protocol entity, and recovery of the first protocol entityoccurs.

In an embodiment, the transceiver unit 730 is further configured to sendsecond indication information to the terminal device, where the secondindication information indicates a sequence number of the first datapacket that is of the first service and that is sent by a first accessnetwork device to the terminal device after the first protocol entity isestablished, the first protocol entity is re-established, or the firstprotocol entity is recovered.

In an embodiment, the transceiver unit 730 is further configured to:receive a data packet sent by a first access network device, where asecond terminal device connected to the first access network device ishanded over from the first access network device to the second accessnetwork device, both the first terminal device and the second terminaldevice perform the first service, and the data packet sent by the firstaccess network device is a data packet of the first service; and sendthird indication information to the first access network device inresponse to a second sequence number of a first protocol layer of a datapacket being sent to the first terminal device is greater than or equalto a first sequence number of a first protocol layer of the data packetthat is sent by the first access network device, where the thirdindication information indicates the first access network device to stopforwarding a data packet to the second access network device.

In an embodiment, the transceiver unit 730 is further configured to:receive status report information that is of a data packet and that issent by the second terminal device, where the status report informationof the data packet indicates, to the second access network device, adata packet successfully received by the terminal device and a datapacket unsuccessfully received by the terminal device; and send fourthindication information to the first access network device based on thestatus report information, where the fourth indication informationindicates a sequence number of the first data packet forwarded by thefirst access network device to the second access network device.

In an embodiment, the transceiver unit 730 is further configured to sendfifth indication information to a first access network device, where thefifth indication information includes a second sequence number N, andthe second sequence number indicates a sequence number of the first datapacket that is of the first service and that is sent by the secondaccess network device to a second terminal device after handover of thesecond terminal device is completed.

In response to the apparatus 700 being configured in the second accessnetwork device or is the second access network device, the modules orthe units in the apparatus 700 are configured to perform the actions orthe processing processes performed by the second access network devicein the foregoing methods. To avoid repetition, detailed descriptions areomitted herein.

In some embodiments, the apparatus 700 is a core network device, or achip or a circuit disposed in the core network device. In response tothe apparatus 700 being the core network device, or the chip or thecircuit disposed in the core network device, the transceiver unit 730 isconfigured to receive a first packet sent by a data server; thetransceiver unit 730 is configured to send a second data packet andfirst indication information to a first access network device, where thefirst indication information indicates a sequence of the second datapacket in at least one data packet sent by the core network device; andthe transceiver unit 730 is configured to send a third data packet andsecond indication information to a second access network device, wherethe first indication information indicates a sequence of the third datapacket in the at least one data packet sent by the core network device,where data in the second data packet and data in the third data packetare the same as data in the first data packet.

In an embodiment, the first indication information includes at least oneof the following information: a general packet radio service tunnelingprotocol-user plane GTP-U sequence number and a first service sequencenumber, where the first service sequence number is set by the corenetwork device or the data server, the first data packet is a datapacket of a first service, and the at least one data packet is a datapacket of the first service.

In response to the apparatus 700 being configured in the core networkdevice or is the core network device, the modules or the units in theapparatus 700 is configured to perform the actions or the processingprocesses performed by the core network device in the foregoing methods.To avoid repetition, detailed descriptions are omitted herein.

For concepts, explanations, detailed descriptions, and other steps ofthe apparatus 700 that are related to the technical solutions providedin embodiments disclosed herein, refer to the descriptions of thecontent in the foregoing methods or other embodiments. Details are notdescribed herein again.

FIG. 9 is a schematic diagram of a structure of a terminal device 800according to embodiments disclosed herein. The terminal device 800performs the actions performed by the terminal device in the foregoingmethod embodiments.

For ease of description, FIG. 9 shows only main components of theterminal device. As shown in FIG. 9 , the terminal device 800 includes aprocessor, a memory, a control circuit, an antenna, and an input/outputapparatus.

The processor is configured to process a communication protocol andcommunication data, control the entire terminal device, execute asoftware program, and process data of the software program, for example,configured to support the terminal device in performing actionsdescribed in the foregoing embodiments of the transmission precodingmatrix indication methods. The memory is configured to store thesoftware program and the data, for example, store the codebook describedin the foregoing embodiments. The control circuit is configured toconvert a baseband signal and a radio frequency signal and process theradio frequency signal. A combination of the control circuit and theantenna is referred to as a transceiver that is configured to send andreceive a radio frequency signal in an electromagnetic wave form. Theinput/output apparatus, for example, a touchscreen, a display, or akeyboard, is configured to: receive data input by a user and output datato the user.

After the terminal device is powered on, the processor reads thesoftware program in the storage unit, interpret and execute instructionsof the software program, and process the data of the software program.In response to data being sent wirelessly, the processor performsbaseband processing on the to-be-sent data, and then outputs a basebandsignal to a radio frequency circuit. The radio frequency circuitperforms radio frequency processing on the baseband signal, and thensends, through the antenna, a radio frequency signal in anelectromagnetic wave form. In response to data being sent to theterminal device, the radio frequency circuit receives a radio frequencysignal through the antenna, converts the radio frequency signal into abaseband signal, and outputs the baseband signal to the processor. Theprocessor converts the baseband signal into data and processes the data.

Persons skilled in the art understands that, for ease of description,FIG. 9 shows only one memory and only one processor. In an actualterminal device, there are a plurality of processors and memories. Thememory is also referred to as a storage medium, a storage device, or thelike. This is not limited in embodiments disclosed herein.

For example, the processor includes a baseband processor and a centralprocessing unit. The baseband processor is configured to process thecommunication protocol and the communication data. The centralprocessing unit is configured to: control the entire terminal device,execute the software program, and process the data of the softwareprogram. Functions of the baseband processor and the central processingunit are integrated into the processor in FIG. 9 . Persons skilled inthe art understand that the baseband processor and the centralprocessing unit each are an independent processor, and areinterconnected by using technologies such as a bus. Persons skilled inthe art understand that the terminal device includes a plurality ofbaseband processors to adapt to different network standards, theterminal device includes a plurality of central processing units toenhance processing capabilities of the terminal device, and componentsof the terminal device are connected by using various buses. Thebaseband processor is alternatively expressed as a baseband processingcircuit or a baseband processing chip. The central processing unit isalternatively expressed as a central processing circuit or a centralprocessing chip. A function of processing the communication protocol andthe communication data is embedded in the processor, or is stored in thestorage unit in a form of the software program. The processor executesthe software program to implement a baseband processing function.

For example, in some embodiments disclosed herein, the antenna and thecontrol circuit that have receiving and sending functions is consideredas a transceiver unit 810 of the terminal device 800, and the processorhaving a processing function is considered as a processing unit 820 ofthe terminal device 800. As shown in FIG. 9 , the terminal device 800includes the transceiver unit 810 and the processing unit 820. Thetransceiver unit is also referred to as a transceiver, a transceiver, atransceiver apparatus, or the like. Optionally, a component that is inthe transceiver unit 810 and that is configured to implement a receivingfunction considered as a receiving unit, and a component that is in thetransceiver unit 810 and that is configured to implement a sendingfunction considered as a sending unit. That is, the transceiver unitincludes the receiving unit and the sending unit. For example, thereceiving unit is also referred to as a receiver, a receiver, or areceiving circuit, and the sending unit is also referred to as atransmitter, a transmitter, or a transmitting circuit.

FIG. 10 is a schematic diagram of a structure of an access networkdevice 900 according to some embodiments disclosed herein. The accessnetwork device 900 is configured to implement functions of the accessdevice (for example, the first access network device, the second accessnetwork device, or a third access network device) in the foregoingmethods. The access network device 900 includes one or more radiofrequency units such as a remote radio unit (remote radio unit, RRU) 910and one or more baseband units (baseband unit, BBU) (which is alsoreferred to as a digital unit, digital unit, DU) 920. The RRU 910 isreferred to as a transceiver unit, a transceiver, a transceiver circuit,a transceiver, or the like, and includes at least one antenna 911 and aradio frequency unit 912. The RRU 910 is configured to send and receivea radio frequency signal, and perform conversion between a radiofrequency signal and a baseband signal, for example, is configured tosend the signaling messages in the foregoing embodiments to a terminaldevice. The BBU 920 is configured to: perform baseband processing,control a base station, and the like. The RRU 910 and the BBU 920 arephysically disposed together, or are physically separated, that is, in adistributed base station.

The BBU 920 is a control center of the base station, and is alsoreferred to as a processing unit, configured to implement a basebandprocessing function such as channel encoding, multiplexing, modulation,or spreading. For example, the BBU (the processing unit) 920 isconfigured to control the base station 40 to perform an operationprocedure related to the network device in the foregoing methodembodiments.

In an example, the BBU 920 includes one or more boards, and a pluralityof boards that jointly support a radio access network (for example, anLTE system or a 5G system) of a single access standard, or separatelysupport radio access networks of different access standards. The BBU 920further includes a memory 921 and a processor 922. The memory 921 isconfigured to store necessary instructions and data. For example, thememory 921 stores the codebook and the like in the foregoingembodiments. The processor 922 is configured to control the base stationto perform a necessary action, for example, configured to control thebase station to perform the operation procedure related to the networkdevice in the foregoing method embodiments. The memory 921 and theprocessor 922 serve one or more boards. In other words, the memory andthe processor are separately disposed on each board. Alternatively, aplurality of boards share a same memory and a same processor. Inaddition, a necessary circuit is further disposed on each board.

In an embodiment, with development of a system-on-chip (system-on-chip,SoC) technology, all or some functions of the parts 920 and 910 areimplemented by using the SoC technology, for example, implemented byusing one base station function chip. The base station function chipintegrates components such as a processor, a memory, and an antennaport. A program of a base station-related function is stored in thememory, and the processor executes the program to implement the basestation-related function. Optionally, the base station function chip canalso read an external memory of the chip, to implement the basestation-related function.

The structure of the access network device shown in FIG. 10 is anembodiment, and does not constitute any limitation on embodimentsdisclosed herein. The embodiments disclosed hereindo not exclude apossibility that a base station structure of another form appears in thefuture.

The processor in embodiments disclosed herein is a central processingunit (central processing unit, CPU). The processor is alternativelyanother general-purpose processor, a digital signal processor (digitalsignal processor, DSP), an application specific integrated circuit(application specific integrated circuit, ASIC), a field programmablegate array (field programmable gate array, FPGA) or another programmablelogic device, a discrete gate or a transistor logic device, a discretehardware component, or the like. The general-purpose processor is amicroprocessor, or the processor is any conventional processor or thelike.

The memory in embodiments disclosed herein is a volatile memory or anonvolatile memory, or includes a volatile memory and a nonvolatilememory. The nonvolatile memory is a read-only memory (read-only memory,ROM), a programmable read-only memory (programmable ROM, PROM), anerasable programmable read-only memory (erasable PROM, EPROM), anelectrically erasable programmable read-only memory (electrically EPROM,EEPROM), or a flash memory. The volatile memory is a random accessmemory (random access memory, RAM), used as an external cache. By way ofexample but not limitative description, random access memories (randomaccess memory, RAM) in many forms is used, for example, a static randomaccess memory (static RAM, SRAM), a dynamic random access memory (DRAM),a synchronous dynamic random access memory (synchronous DRAM, SDRAM), adouble data rate synchronous dynamic random access memory (double datarate SDRAM, DDR SDRAM), an enhanced synchronous dynamic random accessmemory (enhanced SDRAM, ESDRAM), a synchlink dynamic random accessmemory (synchlink DRAM, SLDRAM), and a direct rambus random accessmemory (direct rambus RAM, DR RAM).

All or some of the foregoing embodiments are implemented by usingsoftware, hardware, firmware, or any combination thereof. In response tosoftware being used for implementing embodiments, the foregoingembodiments are implemented completely or partially in a form of acomputer program product. The computer program product includes one ormore computer instructions or computer programs. In response to thecomputer instructions or the computer programs being loaded and executedon the computer, the procedure or functions according to embodimentsdisclosed herein are all or partially generated. The computer is ageneral-purpose computer, a dedicated computer, a computer network, orother programmable apparatuses. The computer instructions are stored ina computer-readable storage medium or are transmitted from acomputer-readable storage medium to another computer-readable storagemedium. For example, the computer instructions are transmitted from awebsite, computer, server, or data center to another website, computer,server, or data center in a wired (for example, infrared, radio, ormicrowave) embodiment. The computer-readable storage medium is anyusable medium accessible by a computer, or a data storage device, suchas a server or a data center, integrating one or more usable media. Theusable medium is a magnetic medium (for example, a floppy disk, a harddisk, or a magnetic tape), an optical medium (for example, a DVD), or asemiconductor medium. The semiconductor medium is a solid-state drive.

Some embodiments disclosed herein further provide a computer-readablemedium. The computer-readable medium stores a computer program. Inresponse to the computer program being executed by a computer, the stepsperformed by the terminal device, the steps performed by the firstaccess network device, the steps performed by the second access networkdevice, or the steps performed by the core network device in any one ofthe foregoing embodiments are implemented.

Some embodiments disclosed herein further provide a computer programproduct. In response to the computer program product being executed by acomputer, the steps performed by the terminal device, the stepsperformed by the first access network device, the steps performed by thesecond access network device, or the steps performed by the core networkdevice in any one of the foregoing embodiments are implemented.

Some embodiments disclosed herein further provide a system on chip. Thesystem on chip includes a communication unit and a processing unit. Theprocessing unit is, for example, a processor. The communication unit is,for example, a communication interface, an input/output interface, apin, a circuit, or the like. The processing unit executes computerinstructions, so that a chip in a communication apparatus performs thesteps performed by the terminal device, the steps performed by the firstaccess network device, the steps performed by the second access networkdevice, the steps performed by the core network device provided in theforegoing embodiments disclosed herein.

Optionally, the computer instructions are stored in a storage unit.

According to the methods provided in embodiments disclosed herein, someembodiments further provide a communication system, including theforegoing first access network device, the foregoing second accessnetwork device, the foregoing core network device, and the foregoingterminal device.

Embodiments disclosed herein are used independently, or are usedjointly. This is not limited herein.

In addition, aspects or features of embodiments disclosed herein areimplemented as a method, an apparatus, or a product that uses standardprogramming and/or engineering technologies. The term “product” usedherein covers a computer program that can be accessed from anycomputer-readable component, carrier, or medium. For example, thecomputer-readable medium includes but is not limited to: a magneticstorage component (for example, a hard disk, a floppy disk, or amagnetic tape), an optical disc (for example, a compact disc (compactdisc, CD) and a digital versatile disc (digital versatile disc, DVD)), asmart card, and a flash memory component (for example, an erasableprogrammable read-only memory (erasable programmable read-only memory,EPROM), a card, a stick, or a key drive). In addition, various storagemedia described in some embodiments disclosed herein indicate one ormore devices and/or other machine-readable media that are configured tostore information. The term “machine-readable media” includes but is notlimited to a radio channel and various other media that can store,include, and/or carry instructions and/or data.

The term “and/or” describes an association relationship betweenassociated objects, and represents that three relationships exist. Forexample, A and/or B represent the following three cases: Only A exists,both A and B exist, and only B exists. The character “/” generallyindicates an “or” relationship between the associated objects. “At leastone” means one or more. “At least one of A and B”, similar to “A and/orB”, describes an association relationship between associated objects,and represents that three relationships exist. For example, at least oneof A and B represents the following three cases: Only A exists, both Aand B exist, and only B exists.

Persons of ordinary skill in the art are be aware that, in combinationwith the examples described in embodiments disclosed in some embodimentsdisclosed herein, units and algorithm steps can be implemented byelectronic hardware or a combination of computer software and theelectronic hardware. Whether the functions are performed by hardware orsoftware depends on particular applications and design constraintconditions of the technical solutions. Persons skilled in the art usedifferent methods to implement the described functions for eachparticular application, but is not to be considered that the embodimentgoes beyond the scope of embodiments disclosed herein.

It is clearly understood by persons skilled in the art that, for thepurpose of convenient and brief description, for a detailed workingprocess of the foregoing system, apparatus, and unit, refer to acorresponding process in the foregoing method embodiments. Details arenot described herein again.

In some embodiments disclosed herein, the disclosed system, apparatus,and method are implemented in other embodiments. For example, theforegoing apparatus embodiments are examples. For example, division intothe units is logical function division and is other division duringactual implementation. For example, a plurality of units or componentsare combined or integrated into another system, or some features areignored or not performed. In addition, the displayed or discussed mutualcoupling, direct coupling, or communication connection are implementedby using some interfaces. The indirect coupling or communicationconnection between the apparatuses or units are implemented inelectrical, mechanical, or another form.

The units described as separate parts are or are not be physicallyseparate, and parts displayed as units are or are not be physical units,that is, are located in one position, or are distributed on a pluralityof network units. Some or all of the units are selected based on actualrequirements to achieve the objectives of the solutions of embodiments.

In addition, functional units in embodiments disclosed herein areintegrated into one processing unit, or each of the units exist alonephysically, or two or more units are integrated into one unit.

In response to the functions being implemented in the form of a softwarefunctional unit and sold or used as an independent product, thefunctions are stored in a computer-readable storage medium. Based onsuch an understanding, the technical solutions disclosed hereinessentially, or the part contributing to the prior art, or some of thetechnical solutions are implemented in a form of a software product. Thecomputer software product is stored in a storage medium, and includesinstructions for instructing a computer device (which is a personalcomputer, a server, or a network device) to perform all or some of thesteps of the methods in embodiments disclosed herein. The foregoingstorage medium includes any medium that can store program code, such asa USB flash drive, a removable hard disk, a read-only memory (Read-OnlyMemory, ROM), a random access memory (Random Access Memory, RAM), amagnetic disk, or an optical disc.

The foregoing descriptions are specific embodiments of embodimentsdisclosed herein, but the protection scope of is not limited thereto.Any variation or replacement readily figured out by persons skilled inthe art within the technical scope disclosed in embodiments shall fallwithin the protection scope of embodiments disclosed. Therefore, theprotection scope of embodiments disclosed shall be subject to theprotection scope of the claims.

1. A communication method comprising: receiving a first data packet anda first core network sequence number from a core network device, whereinthe first core network sequence number is usable to indicate a sequenceof the first data packet in at least one data packet; determining afirst sequence number of a first protocol layer of the first data packetbased on the first core network sequence number; and sending the firstdata packet to a terminal device.
 2. The method according to claim 1,wherein the first core network sequence number is a packet dataconvergence protocol (PDCP) layer sequence number.
 3. The methodaccording to claim 1, wherein the first protocol layer is a packet dataconvergence protocol (PDCP) layer.
 4. The method according to claim 1,wherein the at least one data packet is of a first service, and thefirst service is a multicast service.
 5. The method according to claim1, wherein the determining the first sequence number of the firstprotocol layer of the first data packet based on the first core networksequence number comprises: determining whether a value of the firstsequence number of a first protocol layer of the first data packet isequal to a value of the first core network sequence number.
 6. Themethod according to claim 1, wherein the method further comprises:setting the first sequence number of the first protocol layer of thefirst data packet based on first core network sequence number inresponse to at least one of establishment of a first protocol entity,re-establishment of the first protocol entity, or recovery of the firstprotocol entity occurs.
 7. The method according to claim 1, wherein themethod further comprises: sending indication information to the terminaldevice, wherein the indication information is usable to indicate asequence number of the first data packet that is of the first serviceand that is sent by the first access network device to the terminaldevice after one of the first protocol entity is established, the firstprotocol entity is re-established, or the first protocol entity isrecovered.
 8. A communications apparatus, comprising: one or moreprocessors, and a storage medium configured to store programinstructions; wherein, when executed by the one or more processors, theinstructions cause the communications apparatus to: receive a first datapacket and a first core network sequence number from a core networkdevice, wherein the first core network sequence number is usable toindicate a sequence of the first data packet in at least one datapacket; determine a first sequence number of a first protocol layer ofthe first data packet based on the first core network sequence number;and send the first data packet to a terminal device.
 9. Thecommunications apparatus according to claim 8, wherein_ the first corenetwork sequence number is a packet data convergence protocol (PDCP)layer sequence number.
 10. The communications apparatus according toclaim 8, wherein the first protocol layer is a packet data convergenceprotocol PDCP layer.
 11. The communications apparatus according to claim8, wherein the at least one data packet is of a first service, and thefirst service is a multicast service.
 12. The communications apparatusaccording to claim 8, wherein the determine the first sequence number ofthe first protocol layer of the first data packet based on the firstcore network sequence number comprises: determine whether a value of thefirst sequence number of a first protocol layer of the first data packetis equal to a value of the first core network sequence number.
 13. Thecommunications apparatus according to claim 8, wherein the instructionsfurther cause the apparatus to: set the first sequence number of thefirst protocol layer of the first data packet based on the first corenetwork sequence number in response to at least one of establishment ofa first protocol entity, re-establishment of the first protocol entity,or recovery of the first protocol entity occurs.
 14. The communicationsapparatus according to claim 8, wherein the instructions further causethe apparatus to: send indication information to the terminal device,wherein the indication information is usable to indicate a sequencenumber of the first data packet that is of the first service and that issent by the first access network device to the terminal device after oneof the first protocol entity is established, the first protocol entityis re-established, or the first protocol entity is recovered.
 15. Anon-transitory computer-readable storage medium, comprising executableinstructions, wherein the executable instructions, when executed by acomputer, cause the computer to: receive a first data packet and a firstcore network sequence number from a core network device, wherein thefirst core network sequence number is usable to indicate a sequence ofthe first data packet in at least one data packet; determine a firstsequence number of a first protocol layer of the first data packet basedon the first core network sequence number, wherein; and send the firstdata packet to a terminal device.
 16. The non-transitorycomputer-readable storage medium according to claim 15, wherein_ thefirst core network sequence number is a packet data convergence protocol(PDCP) layer sequence number.
 17. The non-transitory computer-readablestorage medium according to claim 15, wherein the first protocol layeris a packet data convergence protocol PDCP layer.
 18. The non-transitorycomputer-readable storage medium according to claim 15, wherein the atleast one data packet is of a first service, and the first service ismulticast service.
 19. The non-transitory computer-readable storagemedium according to claim 15, wherein the determine the first sequencenumber of the first protocol layer of the first data packet based on thefirst core network sequence number comprises: determine whether a valueof the first sequence number of a first protocol layer of the first datapacket is equal to a value of the first core network sequence number.20. The non-transitory computer-readable storage medium according toclaim 15, wherein the executable instructions further cause theapparatus to: set the first sequence number of the first protocol layerof the first data packet based on the first core network sequence numberin response to at least one of establishment of a first protocol entity,re-establishment of the first protocol entity, or recovery of the firstprotocol entity occurs.